It was a big surprise back in 2008 when 69-year-old John Prescott, the former British deputy prime minister in Tony Blair's Labour government, revealed that he'd recently overcome the bulimia that had begun in his 40s and continued for most of his political career.

His story, publicised widely in the British press at the time, showed a different side of an issue we've come to associate with being young, female and thin. This wasn't a woman doing battle with body image, but a middle aged man who'd found relief from the stress of his job in eating and purging.

Prescott's story is recounted in Midlife Eating Disorders, a new book by US psychiatrist Cynthia Bulik that throws light on a hidden problem - middle aged women and men with eating disorders such as anorexia, bulimia and binge eating disorder.

For some, like Prescott, it's a problem that appears for the first time at midlife but for others it's an old problem that's bounced back - or one that never went away. Troubled relationships, the midlife cocktail of turbulent teens and ageing parents, unemployment, menopause and retirement are all possible triggers that can provoke eating disorders at this age, says Bulik, Professor of Eating Disorders at the University of North Carolina's School of Medicine.

It's a familiar story to psychologist Annabelle Ryburn of Eating Disorders Victoria. Whatever the cause, the symptoms often go unnoticed - partly because midlife eating disorders aren't on our radar and because those who have them no longer live at home with parents looking over their shoulder.

"I've had clients whose eating disorder has resurfaced in middle age often in response to an event like divorce or a difficult family situation," she says. "One client had overcome an eating disorder when she was young but it re-emerged when her children left home and she was faced with a role change that brought back fears about rejection and abandonment.

The important thing to know about treating an eating disorder is that it's not just about getting people to eat more - or less - but to understand the reason why someone may be using eating, purging or restricting food as a coping mechanism, says Ryburn.

"Eating disorders are a sign of a serious mental health problem and if the psychological aspects aren't resolved, people may only partially recover and the eating disorder can be triggered again - or the person may find a different way of attempting to cope like self harm or drug and alcohol abuse. People need the tools to manage the underlying issues like anxiety and difficulties with body acceptance and self worth - issues that aren't exclusive to young people."

How common are midlife eating disorders? It's hard to know because they're often hidden, but although the numbers of middle aged people with anorexia and bulimia are small, around three per cent of women and almost three per cent of men have BED.

As for the cause of these disorders generally, Bulik describes it as a 'soup' of risk factors that includes genetic susceptibility and environment, including changes to how we live that may be contributing to a rise in eating disorders. 'Big Food and Big Beverage' are creating a binge friendly environment, she says, and thanks to bigger portion sizes and the fact that we now eat any time and anyplace, we've lost our compass for normal eating.